1. Field of the Invention
This invention relates to a color cathode-ray tube (CRT) and, more particularly to a color CRT including a luminescent screen assembly.
2. Description of the Background Art
A color cathode-ray tube (CRT) typically includes an electron gun, an aperture mask, and a screen. The aperture mask is interposed between the electron gun and the screen. The screen is located on an inner surface of a faceplate of the CRT tube. The aperture mask functions to direct electron beams generated in the electron gun toward appropriate color-emitting phosphors on the screen of the CRT tube.
The screen may be a luminescent screen. Luminescent screens typically comprise an array of three different color-emitting phosphors (e. g., green, blue, and red). Each color-emitting phosphor is separated one from the other by a matrix line. The matrix lines are formed of a light-absorbing black inert material.
The matrix lines may be deposited on the screen using a shadow mask photolithographic process. In shadow mask photolithographic processes, an image of the aperture mask is formed in a layer of photoresist material coated on the screen, through exposure to ultraviolet (UV) light and resist development in an appropriate developer, providing covered areas and uncovered areas on the screen surface. In a negative photoresist process, covered areas are those areas that are exposed to a substantial dosage of actinic radiation to cause the photoresist to harden and essentially resist developing off of the screen during resist development, while uncovered areas are those where the photoresist is not exposed to an adequate dosage of actinic radiation to cause it to harden and as such the photoresist in the uncovered area will develop off of the screen. For shadow mask lithographic or photoresist processes, the aperture mask is positioned a fixed distance from the screen such that shadows therefrom, projected onto the resist coated screen during exposure to UV light, to define uncovered areas, which will be the intended locations of the matrix lines. After the resist development step, the matrix lines are formed when matrix material is deposited onto uncovered areas of the screen surface.
Conventional aperture masks typically have a transmission of about 18% to about 22%. Recently, in order to increase the color transmission of the screen without increasing the size of the light-emitting phosphors, aperture masks having transmissions of about 40% to about 60% have been incorporated into the color CRT tube. However, the conventional matrix process used for CRTs having the 18% to 22% mask transmission cannot be used in these higher mask transmission CRTs. The reason is that the shadows projected onto the interior faceplate surface from the three conventional source positions (i.e., red, green, and blue source positions) may detrimentally overlap causing misregister of some of the matrix openings with respect to the corresponding electron beams, and in extreme cases matrix lines may not be formed at all (i.e., in cases with higher mask transmissions).
Accordingly, a new method of making the matrix on a luminescent screen is required.
The present invention relates to a method of manufacturing a luminescent screen assembly for a color cathode-ray tube (CRT) having a high transmission mask. The luminescent screen assembly is formed on an interior surface of a faceplate panel of the CRT. The luminescent screen assembly includes a light-absorbing matrix having a plurality of substantially equally sized openings formed therein. The matrix is formed by applying one or more light sensitive layers consisting of a contrast enhancing material and a photoresist hardener on the interior surface of the faceplate panel of the CRT. The one or more light sensitive layers are selectively exposed to a first dosage of radiation that is actinic to the contrast enhancing material projected through openings in a shadow mask, positioned a fixed distance from the screen assembly. The contrast enhancing material obtains greater optical transmission in response to the first dosage such that higher levels of the first dosage cause greater transmission values, wherein transmission specifically refers to a transmission of the contrast enhancing material to a second dosage of radiation. The second dosage of radiation predominantly causes the photoresist to harden and is applied through the mask such that the second dosage aligns with the first dosage. The effective intensity profile of the second dosage will be enhanced in that the ratio of a higher intensity area to a lower intensity area of the second dosage as it propagates through the contrast enhancing material will be at a higher ratio than the corresponding ratio of the actual incident second dosage. Therefore, the contrast enhancing material enables the manufacturer to more easily achieve the targeted dimensions for the hardened and non-hardened photoresist areas. The one or more light sensitive layers in non-hardened regions are removed in a development step. Opaque matrix material is then deposited on the screen surface, followed by removal of the hardened light sensitive layers forming opaque matrix lines on the interior faceplate.
Alternatively, a photoresist layer along with a separate contrast enhancing layer may be used for the one or more light sensitive layers. Additionally, a barrier layer may be deposited to separate the photoresist layer and contrast enhancing layer.